Light emitting diode package having series connected leds

ABSTRACT

Light emitting diode packages as disclosed herein include a monolithic chip including at least a first and a second light emitting diode (LED) that are electrically coupled in series, wherein the first and the second LEDs each include at least one electrical terminal configured to be electrically coupled to a power source. The monolithic chip is mounted onto a connection substrate having first and second landing pads formed from metallic material and electrically isolated from each other. The monolithic chip is mounted to the connection substrate such that the electrical terminal of the first LED is electrically connected to the first landing pad and the electrical terminal of the second LED is electrically connected to the second landing pad. In an example, the monolithic chip includes a third and a fourth LED electrically coupled to each other in series, and electrically coupled to the first and second LEDs in parallel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional of U.S. patent application Ser.No. 14/869,507 filed Sep. 29, 2015, now U.S. Pat. No. 9,853,197 issuedDec. 26, 2017, which claims the benefit of U.S. Provisional PatentApplication No. 62/057,189 filed Sep. 29, 2014, which applications arehereby incorporated by reference in their entirety.

FIELD

Disclosed herein are light emitting diode array constructions, lightemitting diode array packages comprising the same, and methods formaking the same.

BACKGROUND

Light emitting diode (LED) packages for end-use lighting applicationsare known the art. FIG. 1 illustrates an example known LED package 10comprising a single LED 12, which is a lateral or vertical LED,comprising a P contact 14 and an N contact 16 positioned along a topsurface 18 of the LED and on an LED substrate 20, e.g., one that activematerial used to form the P and N junctions is epitaxially grown on. TheLED 12 is disposed on a metal substrate 22 comprising P and N electricalterminals 24 and 26 that are separated from one another and heldtogether by an electrically nonconductive material 28. The LED 12 iselectrically connected with the metal substrate by wires 30 and 32respectively extending from the LED P contact 14 and that is wiredbonded to the metal substrate P terminal 24, and from the LED N contact16 and that is wire bonded to the metal substrate N terminal 26. The LEDmay be encapsulated with a wavelength conversion material 34 tofacilitate light emission from the LED in a particular wavelength.

Arrays of such known LEDs, e.g., two or more lateral or vertical LEDs,may be formed by interconnecting the P contact of one LED to an Ncontact of an adjacent LED in series by wires extending along the topsurface of the LEDs. FIG. 2 illustrates an array 40 of known LEDs, e.g.,a 3×3 array of lateral or vertical LEDS, wherein the LEDs 42 in thearray are connected with in series to one another by wires 44 extendingalong the top surface between the P and N contacts of adjacent LEDs. Theserially connected LEDs are then connected in parallel to the metalsubstrate by a wire 46 extending from the P contact of a first LED inthe series to the P terminal 48 of the metal substrate, and a wire 50extending from the N contact of a last LED in the series to the Nterminal 52 of the metal substrate.

A feature of such known LED package is that they are costly to makegiven the time and labor associated with forming the wired connectionsfrom the LED to the metal substrate and, in an array configurationadditionally with forming the wired serial electrical connectionsbetween the individual LEDs. Further, such LED packages are known tohave less than optimal thermal properties, as the LED or LEDs in anarray generate a large amount of heat when powered, which heat largelyremains in the LED and is not efficiently extracted or removed therefromduring operation, thereby operating to reduce LED service life andreduce the service life of lighting devices or assemblies comprising thesame.

It is, therefore, desired that LED package be constructed in a mannerthat is both cost efficient to make, and that has improved thermalperformance properties when compared to such above-described LEDconstructions and packages.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of light emitting diodeconstructions, assemblies comprising the same, and methods for makingthe same as disclosed herein will be appreciated as the same becomesbetter understood by reference to the following detailed descriptionwhen considered in connection with the accompanying drawings.

FIG. 1 is a cross-sectional side view of a known light emitting diodepackage;

FIG. 2 is a top view of a known light emitting diode array package;

FIG. 3 is a cross-sectional side view of an example monolithic lightemitting diode array package as disclosed herein;

FIG. 4 is a perspective view of an example monolithic light emittingdiode array as disclosed herein;

FIG. 5 is a bottom view of an example monolithic light emitting diodearray as disclosed herein; and

FIG. 6 is a perspective side view of an example monolithic lightemitting diode array package as disclosed herein.

SUMMARY

Light emitting diode packages as disclosed herein comprise a monolithicchip including at least a first and a second light emitting diode (LED)that are electrically coupled in series. The first and the second LEDseach include at least one electrical terminal configured to beelectrically coupled to a power source. In an example embodiment, LEDsare flip chip LEDs and the electrical terminals extend along a commonsurface of the LEDs. The monolithic chip is mounted onto a connectionsubstrate that includes first and second landing pads which are formedfrom a metallic material and that are electrically isolated from eachother. In an example, the connection substrate includes a siliconematerial interposed between the first and second landing pads andextending around and edge of the connection substrate. The monolithicchip is mounted to the connection substrate such that the electricalterminal of the first LED is electrically connected to the first landingpad and the electrical terminal of the second LED is electricallyconnected to the second landing pad. In an example, the monolithic chipincludes a third and a fourth LED electrically coupled to each other inseries, and electrically coupled to the first and second LEDs inparallel. In such example, the first and second terminals operate toprovide the parallel electrical connection between the LEDs.

LED packages as disclosed herein are made by the steps of forming amonolithic wafer comprising a number of LEDs. Forming a serieselectrical connection between LEDs that are oriented in a sting, andforming a parallel electrical connection between LEDs in the string,wherein the steps of forming the series and parallel electricalconnections are done at the wafer level. In an example, the monolithicwafer may have two or more strings of serially connected LEDs, and theparallel electrical connection between LEDs in the two or more stringsmay be provided by first and second electrical terminals formed on themonolithic wafer. The so-formed wafer is then connected with theconnection substrate so that the first and second electrical terminalsare in contact with the connection substrate first and second landingpads to both provide an electrical connection therebetween, and tofacilitate the transfer of heat or thermal energy from the monolithicwafer during operation of the LED package to thereby provide improvedthermal operating efficiency and performance.

DETAILED DESCRIPTION

Light emitting diodes (LEDs) and packages comprising the same asdisclosed herein are specially constructed having a flip chiparchitecture configured to promote use in an array and packaging with ametal connection substrate in a manner that is both cost efficient andthat provides improved thermal properties when compared to theconventional LED packages discussed above.

FIG. 3 illustrates an LED package 60 as disclosed herein comprising amonolithic wafer or die 61 comprising one or more LEDs. In an example,the monolithic die may include a single LED and the LED may be a flipchip LED comprising P and N contacts 64 and 66 that are disposed along acommon surface of the LED. In such embodiment, the LED comprises atransparent substrate 68 through which light is emitted upon poweringthe LED, wherein the P and N contacts are positioned along a surface ofthe LED opposite a top surface 71 of the transparent substrate 68. Theflip chip LED may be formed by conventional technique, e.g., byepitaxially depositing a desired active material onto a compatiblesubstrate material. In an example, the active material may be selectedproduce light in a blue wavelength in the range of from about 400 to 500nm, herein referred to as a blue flip chip LED. In an example, the blueflip chip LED comprises an active material formed for example from GaNthat has been grown, e.g., epitaxially grown, onto a transparentsubstrate such as one formed from sapphire or the like having acrystalline lattice structure that is compatible with the activematerial, e.g., GaN. This is but one example of the type of activematerial and substrate that can be used to form flip chip LEDs usefulfor forming LED packages as disclosed herein, and it is to be understoodthat such example is provided for references and that the types of flipchip LEDs within the scope of the concept as disclosed herein are notlimited as to the types of active materials or substrates that may beused to form the same. The LED may be encapsulated with a wavelengthconverting material 69 such as conformal phosphor or the like for thepurpose of converting the wavelength of light produce by the LED to adesired wavelength for an end-use application.

The LED P and/or N contacts 64 and 66 may be fanned out, or theirrespective surface area enlarged/expanded, so as to form P and/or Nterminals to facilitate connection with respective P and N terminals orcontact pads 70 and 72 of a connection substrate 74 used both toaccommodate mechanical attachment of the LED and provide electricalpower thereto. In an example, the LED P and N contacts or terminals 64and 66 are sized to both facilitate a desired electrical contact withthe respective connection substrate P and N terminals or contact pads 70and 72, and to facilitate a desired level of heat or thermal transferfrom the LED to the connection substrate to provide an improved level ofthermal properties, improving the service life of the LEDs and thepackage comprising the same. In an example, the P and N terminals 70 and72 of the connection substrate are formed from a metallic material suchas copper or the like.

As illustrated in FIG. 3, the P and N terminals 70 and 72 of theconnection substrate 74 are separated from one another by anelectrically insulating material 73, which in an example embodiment maybe a polymeric material such as silicone or the like. In an example,open spaces 75 may exist between the electrically insulating material 73and the LED P and N contacts 64 and 66. An electrically insulatingmaterial 73 is also disposed along outer edges of the P and N terminals70 and 72 and operates both to insulate the outer edges and to hold theP and N terminals together. In an example, the electrically insulatingmaterial disposed along the outer edges of the conductive substrate maybe formed from the same material used to separate the P and N terminals.In an example, the connection substrate comprising the P and Nterminals, the insulating material interposed therebetween, and theinsulating material disposed around the edge of the P and N terminals,may be formed by a molding process.

Example LED packages as disclosed herein may comprise a single LED or anumber of LEDs connected with the connection substrate. In an examplewhere the LED package comprises a single LED, such LED comprises asingle P contact and single N contact that is placed into contact withthe respective P and N terminal of the connection substrate. In anexample where the LED package comprises a number of LEDs, such LEDs maybe provided in combined form as a monolithic wafer or die, wherein themonolithic wafer comprises a number of P and N contacts associated witheach LED, and wherein the P and N contacts are disposed along a commonwafer surface.

FIG. 4 illustrates a monolithic wafer 80 comprising an array of LEDs 82,and in an example embodiment the LEDs are flip chip LEDs. In theillustrated example, the monolithic wafer comprises a 4×4 array of LEDsor 16 LEDs. However, it is to be understood that the number andarrangement of LEDs in the monolithic wafer may be other than thatdisclosed and illustrated. For example, the monolithic wafer maycomprise two or more LEDs that are oriented extending along a commonaxis, or may comprise two or more LEDs that are oriented along a firstaxis and a second axis perpendicular to the first axis, e.g., in anarray where the LEDs in the array are in a series-parallel electricalconnection. The particular number and arrangement of LEDs within themonolithic wafer is understood to vary depending on the particularend-use application.

In example illustrated in FIG. 4, the monolithic wafer 80 comprises Pand N terminals 84 and 86 extending along a common surface of the waferopposite the wafer substrate top surface 88. The P and N terminalsextend in a direction parallel with one another and are in parallelelectrical connection with respective P contacts of terminal LEDspositioned at one end of the array, and are in parallel electricalconnection with respective N contacts of terminal LEDs positioned at anopposite end of the array. As described above, the P and N terminals 84and 86 may be configured to provide both a desired degree of electricalcontact with the connection substrate, and a desired degree of thermaltransfer from the LED array to the connection substrate to therebyprovide improved thermal performance properties during operation.

FIG. 5 illustrates an underside surface 90 of the monolithic wafer 80 ofFIG. 4 prior to forming the P and N terminals (84 and 86 with referenceto FIG. 4). A feature of LED packages as disclosed herein, comprisingthe use of a monolithic wafer having a number of LEDs, is the ability toprovide a desired series and parallel electrical connection between theLEDs on the wafer itself, i.e., at the wafer level thereby avoiding thecosts and labor associated with making such connections by wire bondingamong individual LEDs, i.e., after the wafer has been diced to form theseparate LEDs. In an example, a series electrical connection is madebetween the LEDs in each of the rows extending along a common first axis96 by connecting P contacts 92 of an LED in each row with N contacts 94of an adjacent LED in the same row. The series electrical connectionbetween the P and N contacts within a row can be made by wire connection95, by electrically conductive vias formed in the wafer, or by otherelectrically conductive element. In an example, the underside surface 90may comprise recessed regions 97 extending along the wafer betweenadjacent LEDs in series connection. Again, a feature of the concept asdisclosed herein is that such electrical connections between the LEDsare being done at the wafer level.

The array includes terminal LEDs 98 positioned at one end 100 of eachrow running along axis 96 that comprises a P contact 102, and includesterminal LEDs 104 positioned at an opposite end 106 of each row runningalong axis 96 that comprises an N contact 108. The LEDs in the rowsrunning along axis 96, and that are in series electrical connectionwithin the row, are placed into parallel electrical connection with eachother by connecting together the P and N contacts 102 and 108 of the endLEDs 98 and 104, wherein the parallel connection extends along the axis110, which is perpendicular to axis 96. Such parallel electricalconnection can be made in the same manner as was done to provide theseries electrical connection between the LEDs, e.g., by wire connection,electrically conductive vias formed in the wafer, or by otherelectrically conductive element, again all taking place at the waferlevel. In an example, such parallel connection between the P and Ncontacts 102 and 108 is made by configuring such respective P and Ncontacts to connect with one another to form a respective P and Nterminal (as illustrated in FIG. 4), e.g., by fanning out, enlarging orexpanding the contact configurations. Alternatively, such parallelconnection between the P and N contacts 102 and 108 can be made throughthe use of separate metallic electrodes that are configured to beattached with each of the respective P and N contacts 102 and 108, whichelectrodes thereby form the P and N terminals for the monolithic wafer.The monolithic array and/or the P and N terminals are configured in sucha manner so that the P and N terminals do not make direct contact withrespective N and P contacts of the LEDs in the array.

FIG. 6 illustrates an example LED package 200 as disclosed hereincomprising monolithic wafer 202 as disclosed above with reference toFIGS. 4 and 5, comprising a plurality of LEDs 204, e.g., flip chip LEDs,forming an array that is in series-parallel electrical connection alonga common surface 206 opposite a top surface 208 of the wafer, which is atop surface of a transparent substrate 212. The common surface 206comprising recessed regions 297 (shown as 97 in FIG. 4). The monolithicwafer comprises a P terminal 214 and an N terminal 216 that areconfigured to provide a desired degree of electrical contact withrespective P and N terminals or landing pads 218 and 220 of theconnection substrate 222 to power the LED array, and to provide adesired degree of heat transfer from the LED array during operation. Theconnection substrate P and N landing pads 218 and 220 are separated fromone another by the electrically insulating material 273, and theelectrically insulating material 273 is also disposed along outer edgesof the P and N landing pads 218 and 220 to insulate the outer edges ofthe LED package.

A feature of LED packages as disclosed herein is that the LEDs containedtherein are provided in the form of a monolithic wafer and theelectrical circuitry between the LEDs is formed at the wafer level,thereby reducing production costs. Further, LED packages as disclosedherein comprise flip chip LEDs having P and N terminals disposed along acommon surface to facilitate attaching the monolithic LED array torespective P and N terminals or landing pads of a connection substratewafer. The ability to physically connect the monolithic LED array to theconnection substrate through the P and N terminals enables for thethermal transfer of heat from the LED array during operation, therebyproviding improved thermal performance properties when compared to theconventional LED packages disclosed above.

Although certain specific embodiments of LED packages have beendescribed and illustrated for purposes or reference, it is to beunderstood that the disclosure and illustrations as provided herein notlimited to the specific embodiments. Accordingly, various modifications,adaptations, and combinations of various features of the describedembodiments can be practiced without departing from the scope what hasbeen disposed herein including the appended claims.

What is claimed is:
 1. A method for making a light emitting diode (LED)package comprising the steps of: forming a monolithic wafer comprising anumber of LEDs each having P and N contacts; forming two or more stringsof LEDs, wherein the LEDs within each string have P and N contacts thatare in series connection with one another; forming a parallel connectionbetween the LEDs in the two or more strings by connecting together the Pcontacts of an LED from each string, and connecting together the Ncontact of an LED from each string, wherein the parallel P connectioncomprises a P terminal extending from the monolithic wafer, and whereinthe parallel N connection comprises an N terminal extending from themonolithic wafer; and placing the monolithic wafer onto a connectionsubstrate so that the P terminal is in contact with a P landing pad ofthe connection substrate and the N terminal is in contact with an Nlanding pad of the connection substrate, wherein the P and N landingpads are electrically isolated from one another.
 2. The method asrecited in claim 1 wherein the LEDs are flip chip LEDs, and wherein Pand N terminals extend from a common surface of the monolithic waferopposite from a transparent substrate of the monolithic wafer.
 3. Themethod as recited in claim 1 wherein the N and P terminal and the N andP landing pads are all formed from a metallic material, and whereinbefore the step of placing, the connection substrate is formedcomprising a silicone material interposed between the P and N landingpads.
 4. The method as recited in claim 1 wherein before or after thestep of placing, the connection substrate comprises an electricallyisolating material disposed around an outside edge of the connectionsubstrate.
 5. The method as recited in claim 1 wherein the step offorming the two or more strings of LEDs and the step of forming aparallel connection takes place when the LEDs are in the form of themonolithic wafer.
 6. The method as recited in claim 1 furthercomprising, after the step of placing, disposing a wavelength conversionmaterial onto the monolithic wafer.
 7. A method of making a monolithicwafer comprising an array of light emitting diodes (LEDs) inseries-parallel electrical connection with one another, the methodcomprising the steps of: electrically connecting a number of flip chipLEDs together in series to form a string of flip chip LEDs extendingalong the wafer, wherein the wafer comprises two or more of the stringsof LEDs in series electrical connection; and electrically connectingfirst ends of the strings of the flip chip LEDs in parallel with oneanother by a first electrical terminal, and electrically connectingsecond ends of the strings of the flip chip LEDs in parallel by a secondelectrical terminal thereby forming series-parallel electricalconnection between the LEDS.
 8. The method as recited in claim 7 whereinthe first electrical terminal is in parallel electrical contact with Pcontacts of the LED strings, and the second electrical terminal is inparallel electrical contact with N contacts of the LED strings.
 9. Themethod as recited in claim 7 wherein one or more of the LEDs produceslight in a wavelength of from about 400 to 500 nm.
 10. The method asrecited in claim 7 wherein one or more of the LEDs comprise an activematerial formed from GaN grown onto a transparent substrate.
 11. Themethod as recited in claim 7 wherein the first and second electricalterminals are sized larger than electrical contacts of the respectiveLEDs that the first and second electrical terminals are connected with.12. The method as recited in claim 7 wherein the strings of LEDs inseries electrical connection with one another run along the waferparallel to a first axis of direction, and wherein the LEDs connected inparallel run along the wafer parallel to a second axis of direction thatis perpendicular to the first axis of direction.
 13. The method asrecited in claim 7 further comprising the step of connecting the LEDarray to connection substrate, wherein the connection substratecomprises first and second landing pads that are sized and positioned tomake electrical contact with respective first and second electricalterminals of the LED array.
 14. The method as recited in claim 13,wherein before the step of connecting, the connection substrate isformed to include an electrically insulating material interposed betweenthe first and second landing pads.
 15. The method as recited in claim13, wherein before or after the step of connecting, an electricallyinsulating material is disposed around an outside surface of theconnection substrate.
 16. A method of making a light emitting diode(LED) package comprising the steps of: connecting a plurality of flipchip LEDs on a monolithic wafer series-parallel electrical connection toform an LED array, wherein the LED comprises a first electrical terminaland a second electrical terminal each in respective parallel connectionwith strings of LEDs, wherein the LEDs within the strings are in seriesconnection with one another; and connecting the LED array to aconnection substrate, wherein the array first and second electricalterminals are in electrical contact with respective first and secondlanding pads of the connection substrate to form the LED package. 17.The method as recited in claim 16 wherein before the step of connectingthe LED array to the connection substrate, the connection substrate isformed having an electrically insulating material interposed between thefirst and second landing pads.
 18. The method as recited in claim 16wherein before or after the step of connecting the LED array to theconnection substrate, the connection substrate is formed having anelectrically insulating material disposed along an outside edge of theconnection substrate.
 19. The method as recited in claim 16 wherein thestrings of LEDs extend along the wafer in a direction parallel with afirst axis, and the first and second electrical terminals extend alongthe wafer in a direction perpendicular to the first axis.
 20. The methodas recited in claim 16 wherein the first and second electrical terminalsare sized larger than electrical contacts of the respective LEDs thatthe first and second electrical terminals are connected with.